1. Field of the Invention
The present invention relates to an ink jet, printing apparatus and a wiping method therefor, and more specifically, to the construction of a blade used for a wiping operation performed as one of processes for maintaining the ejection performance of a printing head from which ink is ejected.
2. Description of the Related Art
Ink jet printing apparatuses have the advantages of low noise, low running costs, an easy reduction in size of the apparatus, easy introduction of various colors, and the like, and are applied to printers, facsimile terminal equipment, copy machines, and the like.
A printing head used in such an apparatus includes ejection openings as openings through which ink is ejected. In general, according to an ejection signal based on print data transmitted by a host apparatus such as a personal computer, the ink jet printing apparatus drives the printing head to eject ink droplets through the ejection openings. The size of these ejection openings, if they are, for example, circular, is such that their diameter is about several tens of μm, and tends to be reduced in order to improve the quality of images to be printed or the like. Thus, the ejection openings have been more and more densely arranged.
Since the ink jet system-based printing apparatus causes ink to be ejected through these fine ejection openings, the ejection openings are prone to be blocked, and the range within which the fluidity (viscosity) of the ink may vary is relatively small. Thus, the ink jet printing apparatus generally executes recovery processes in order to prevent blockage or an increase in viscosity of the ink or to resolve it if it actually occurs, thereby keeping the ink ejection performance of the printing head of an acceptable quality.
One of these recovery processes is a capping operation, which uses a cap to cover a surface of the printing head in which the ejection openings are formed while no printing operation is performed or in other cases. When no ink is ejected, for example, when no printing operation is performed, a certain amount of ink located close to the ejection openings may be more viscous or in an extreme case, may be dried and solidified, owing to evaporation of an ink solvent associated with the temperature, humidity, or the like of the environment in which the apparatus is located. Such an increase in viscosity of the ink may cause inappropriate ejection such as a reduced amount of ejection or deflected or hindered ejection, thereby reducing print grade. The capping operation prevents such a phenomenon.
Another recovery process is a so-called suction recovery process, which forcibly removes extremely viscous ink causing blockage, solidification, or the like. More specifically, the above-described cap is contacted to the surface of the printing head on which the ejection openings are disposed, and a pump or the like is used to reduce the pressure in the cap to discharge the more viscous ink via the ejection openings. In this respect, the pumping system is roughly classified into two types. One type is a cylinder type in which a piston is moved to generate a relatively high negative pressure. The other type is a tube pump type in which a roller is used to squeeze a tube so that the restoring force of the tube induces negative pressure.
As a further recovery process, a so-called preliminary ejection is known. During printing, ink may not be ejected through all the ejection openings, and, depending on printing data, no ink may be ejected through some of the ejection openings for some time. In these ejection openings, ink further becomes more viscous because no ejection is performed and viscous ink is not removed. To prevent this situation, the preliminary ejection is carried out so that ink is ejected into a cap or the like through all or some of the ejection openings in the printing head to refresh the interior of the ejection openings, for example, every specified lapse of time or each time a specified amount of printing is executed. If ink is preliminarily ejected into the cap, then the above-described pump is actuated to suck and discharge the ink from the cap when the amount of preliminarily-ejected ink reaches a certain value.
In addition to the above-described recovery processes using the cap, known recovery processes include a wiping process of using a blade to wipe the surface of the printing head on which the ejection openings are disposed.
Paper dust or other dust from a printing paper located opposite the printing head, or ink mist resulting from ink ejected onto and bouncing off the printing paper, may stick to the surface of the printing head on which the ejection openings are disposed. In this case, when such paper dust or ink mist stick to the fine ejection openings, ink cannot be ejected or is inappropriately ejected. To prevent ink from being inappropriately ejected, a wiping operation is performed by contacting the blade against the ejection opening-disposed surface of the printing head to wipe the surface at predetermined timings during printing, for example, after a specified time has passed or a specified amount of printing has been carried out. This enables removal of the paper dust or ink mist sticking to the above-mentioned surface. The wiping operation is also performed in response to a user's instruction operation if the user observes a printed image degraded as a result of inappropriate ejection.
Further, the wiping operation can be associated with the other recovery processes described above. That is, in the above-described preliminary ejection or suction recovery process, ink is ejected into the cap, or with the cap contacted to the ejection opening-disposed surface the printing head, the pressure in the cap is reduced for suction. Thus, after these recovery processes, the ink may remain stuck to the cap. Then, during the next recovery process, the cap, to which the ink remains stuck, is contacted to the ejection opening-disposed surface of the printing head to transfer the ink to this surface. Because of this, the wiping operation is also performed after the printing head is released from contact of the cap.
The construction of the printing head, the direct object of the above-described recovery process, needs to be adapted to the recent increased grade of printed images, for example, the increased density of black characters or the like, introduction of multiple colors, increased definition (resolution), improved waterproofness, and the like.
In general, serial system-based ink jet printing apparatuses have a printing head mounted on a carriage so that in response to the reciprocation of the carriage, ink is ejected from the printing head to form dots on printing paper for printing. With this system, a printing head that inexpensively meets requirements for an increase in printing grade is preferred for use in ejecting black ink to react with other color inks to insolubilize these inks, and has dense arrays of ejection openings. An example of such a construction is shown in FIG. 8.
FIG. 8 is illustration schematically showing the surface of the printing head on which the ejection openings are disposed. As shown in this figure, a printing head 7 has an ejection opening array 23 for black (Bk) ink, an ejection opening array 24 for yellow (Y) ink, an ejection opening array 25 for magenta (M) ink, and an ejection opening array 26 for cyan (C) ink, which are arranged parallel with one another in a scanning direction of the printing head 7. In this figure, for illustrative simplification, the individual ejection openings are not shown, but each array of a plurality of ejection openings is shown as a line. This is applicable to the subsequently-described figures.
The pitch between the ejection openings in each ejection opening array is equivalent to 600 dpi (dots per inch) for increased resolution or 1200 dpi for further increased resolution. The pitch between the ejection opening arrays is also tending to be decreased in order to reduce the size of the printing head and thus the apparatus. Further, the array width of the group of ejection opening arrays for the respective inks is about 3.5 mm, corresponding to a relatively dense construction.
As a construction of a printing head that meets the requirements for high-grade printing, in view of improving waterproofness or of preventing bleeding between the colors, the printing head is known which uses inks, for example, in which chemical reaction occurs between black ink and other color inks to make dyes or the like insoluble. For example, the black ink is cationic, whereas the other color inks are anionic. This causes the black ink and the other color inks for printing a black character or the like to be ionically coupled together to make color materials such as dyes insoluble, thereby improving the waterproofness of printed black characters or the like. Further, this can prevent bleeding between a black printed area and a color printed area.
However, when the printing head, in which the ejected black ink and other color inks are made insoluble through mixture as described above, is one of a reduced size, a pitch between the ejection opening array for black ink and the ejection opening arrays for the other color inks becomes small, and then the following problems may occur with a wiping operation using a blade as described previously.
As described previously, to prevent ink from being inappropriately ejected as a result of ink mist or the like sticking to the ejection opening-disposed surface of the printing head, a wiping operation is performed using a blade. FIGS. 9A and 9B are schematic illustrations showing a conventional example of an arrangement for wiping. As shown in these figures, a single blade 27 is moved in the direction in which the ejection opening array for each color extends, to perform a wiping operation. This is to prevent the black ink and other color inks, which react with each other to be made insoluble, from being mixed together as a result of the wiping operation. More specifically, this prevents a part of the blade 27 which wipes the ejection opening array 23 for the black ink from overlapping parts thereof which wipe the ejection opening arrays 24, 25, and 26 for the other color inks.
However, even with this construction, when the ejection opening-disposed surface of the printing head is wiped using the single blade 27, both the black ink and the other color inks may be brought to the center of the blade and mixed together as the blade 27 is moved, as shown by reference numeral 28 in FIGS. 9A and 9B. Consequently, reaction may occur to generate insoluble matter, or the black ink may enter the ejection openings of the color inks or, conversely, the color inks may enter the ejection openings of the black ink. As a result, the insoluble matter may stick to the vicinity or inside of the ejection openings, which are then blocked and ink may be inappropriately ejected or may not be ejected therethrough.
For example, Japanese Patent Application Laid-open No. 7-223321 (1995) describes a wiping construction that prevents inks of different colors from being brought together and mixed in the center of the blade as shown in FIGS. 9A and 9B. That is, this document describes the provision of a plurality of blades, each corresponding to one of the ejection opening arrays for the respective colors. More specifically, for a printing head in which the ejection opening arrays for the respective colors are arranged to form one line, which differs from the ejection opening arrays shown in FIG. 8, a blade is provided for each ejection opening array and is composed of two blade parts arranged so as to be V-shaped and to have an overlapping portion so that wiped-away ink is moved toward a narrower part of the V shape. This enables wiped-away inks to be moved to their respective locations where they are not mixed together.
However, such a wiping construction has an arrangement in which wiping of the blade is executed in a direction perpendicular to each ejection opening array in such a manner as to cover all the ejection openings, so that the “V” shape of the blade must have an overlapping portion in the wiping direction as described above. Thus, certain amounts of inks moved toward the center (in this document, inks of the same color) may be mixed together. Further, if the blade described in the document is to be applied to a printing head having ejection opening arrays such as those shown in FIG. 8, the ejection opening arrays 23 to 26 for the respective colors are each provided with the V-shaped blade, so that the space between the ejection opening arrays is too large to reduce the size of the printing head.